ItemsContextExtensions.cs

namespace MyProject.Extensions
{
    public static class ItemsContextExtensions
    {
        public static Item Get(this ItemsContext source, string identifier)
        {
            if (string.IsNullOrWhiteSpace(identifier))
                throw new Exception("Must set identifier for getting global property");

            var dictionary = source as IDictionary;

            if (!dictionary.Contains(identifier))
                return null;

            var value = dictionary[identifier];

            if (value.GetType() == typeof(Item))
            {
                return value as Item;
            }

            if (!(value.GetType() == typeof(Func<Item>)))
                return null;

            var lazyValue = value as Func<Item>;

            var resultValue = lazyValue() as Item;

            dictionary[identifier] = resultValue;

            return resultValue;
        }

        public static void SetLazy(this ItemsContext source, string identifier, Func<Item> lazyValue)
        {
            if (string.IsNullOrWhiteSpace(identifier))
                throw new Exception("Must set identifier for setting global property");

            var dictionary = source as IDictionary;

            dictionary[identifier] = lazyValue;
        }
    }
}